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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8674) Improve performance of postponed block scans
Date Thu, 01 Dec 2016 18:42:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15712703#comment-15712703
] 

Hudson commented on HDFS-8674:
------------------------------

SUCCESS: Integrated in Jenkins build Hadoop-trunk-Commit #10924 (See [https://builds.apache.org/job/Hadoop-trunk-Commit/10924/])
HDFS-8674. Improve performance of postponed block scans. Contributed by (kihwal: rev 96c574927a600d15fab919df1fdc9e07887af6c5)
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java


> Improve performance of postponed block scans
> --------------------------------------------
>
>                 Key: HDFS-8674
>                 URL: https://issues.apache.org/jira/browse/HDFS-8674
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.6.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>             Fix For: 2.8.0, 3.0.0-alpha2
>
>         Attachments: HDFS-8674.2.patch, HDFS-8674.branch-2.patch, HDFS-8674.patch, HDFS-8674.patch,
HDFS-8674.trunk.2.patch, HDFS-8674.trunk.patch
>
>
> When a standby goes active, it marks all nodes as "stale" which will cause block invalidations
for over-replicated blocks to be queued until full block reports are received from the nodes
with the block.  The replication monitor scans the queue with O(N) runtime.  It picks a random
offset and iterates through the set to randomize blocks scanned.
> The result is devastating when a cluster loses multiple nodes during a rolling upgrade.
Re-replication occurs, the nodes come back, the excess block invalidations are postponed.
Rescanning just 2k blocks out of millions of postponed blocks may take multiple seconds. During
the scan, the write lock is held which stalls all other processing.



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